The recent trends of cutting work include the demand for dry work dispensing with a cutting oil agent from the standpoint of global environmental protection, the increasing variety of workpieces to be cut, and the increasing cutting speed with the aim of further improving the work efficiency, for example. Accordingly, the cutting tool used for cutting work tends to have a higher temperature of its cutting edge during cutting work, and characteristics required of the tool material are becoming increasingly severer.
In particular, a coating (also called ceramic coating or hard layer for example) formed on the surface of the tool is a significantly important factor for meeting such requirements for characteristics of the tool material. The required characteristics of such a coating include, in addition to high hardness (wear resistance) and high-temperature stability (oxidation resistance), strong adherence to the base material.
In order to improve the adherence of the coating to the base material, Japanese Patent Laying-Open No. 05-237707 (PTD 1) proposes to form a plurality of coatings on a base material made of a cemented carbide and diffuse W and Co in the first coating. Japanese Patent Laying-Open No. 2002-331403 (PTD 2) proposes to form projections on the surface of a base material and segregate a coating on grain boundaries of the projections, thereby achieving an anchor effect.